Tunable pinning in superconducting films with magnetic microloops

Silhanek, Alejandro; Gillijns, Werner; Moshchalkov, Victor; Metlushko, V.; Ilić, B.

doi:10.1063/1.2374798

Cited by 29 publications

(35 citation statements)

References 15 publications

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“…Interestingly, when these rings are placed in close proximity to a superconducting layer, either a strong vortex pinning or weak pinning can be obtained by simply switching from onion to flux-closure state, respectively. Although the influence of these magnetic templates on the vortex pinning is relatively well understood [23], little is known about their influence on the vortex dynamics.…”

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Switchable magnetic dipole induced guided vortex motion

Verellen

Silhanek

Gillijns

et al. 2008

Applied Physics Letters

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We present evidence of magnetically controlled guided vortex motion in a hybrid superconductor/ferromagnet nanosystem consisting of an Al film on top of a square array of permalloy square rings. When the rings are magnetized with an in-plane external field H, an array of point-like dipoles with moments antiparallel to H, is formed. The resulting magnetic template generates a strongly anisotropic pinning potential landscape for vortices in the superconducting layer. Transport measurements show that this anisotropy is able to confine the flux motion along the high symmetry axes of the square lattice of dipoles. This guided vortex motion can be either re-routed by 90 degrees by simply changing the dipole orientation or even strongly suppressed by inducing a flux-closure magnetic state with very low stray fields in the rings. During the last years there has been a considerable effort to conceive and realize new superconducting devices that allow to modulate locally the magnetic fields practically at will [1]. These systems rely essentially on either static arrays, such as pinning centers [2,3,4,5] and vortex-antivortex generators [6,7], or components influencing the vortex dynamics like channels [8,9,10,11] and ratchets [12,13]. The ultimate motivation behind the manipulation of the local vortex density is to enhance the performance of superconductor-based devices by reducing the noise in squid-based systems [14,15], gaining control on superconducting THz emitters [16] or even providing a way to predefine the optical transmission through the system [17].Unfortunately, for the majority of the components used in fluxonics devices, once they are created there is no margin for further modifications. In some cases this lack of flexibility becomes a limiting factor in the performance of the devices. For instance, a predefined ratchet system designed to effectively remove vortices from a specific location can work properly at low fields but ignores the inevitable reversed ratchet at higher fields thus making its functionality rather impractical [12,13,18,19]. A way to circumvent this shortcoming can be worked out by introducing magnetic pinning centers which have additional internal degrees of freedom not available in conventional nanostructured pinning sites or defects created via irradiation.In this work we demonstrate that reversible and switchable guidance of the vortex motion can be achieved using a square array of magnetic square rings lying underneath a superconducting film. Transport measurements unambiguously show that the vortex dynamics is fully dominated by the magnetic landscape generated by the ring structures. When the magnetic unit cell is rotated 45 degrees off the Lorentz force F L the average vortex velocity v follows the direction of the principal axis of the magnetic lattice rather than the driving force. This channeling effect can be easily suppressed when inducing a nearly isotropic pinning landscape by setting the square rings in a flux-closure state with very low stray fields.The two samples used f...

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confidence: 99%

Switchable magnetic dipole induced guided vortex motion

Verellen

Silhanek

Gillijns

et al. 2008

Applied Physics Letters

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“…In addition to the ratchet effect, these superconducting-magnetic hybrids exhibit a variety of other interesting effects such as quantum matching phenomena in which periodic matching is observed in the flux flow resistance or bistable superconductivity which depends on the magnetic history. [7][8][9][10][11] A widely investigated ratchet of this type consists of a superconducting film in proximity to a square array of triangular magnetic nanostructures. For triangles arranged with one edge parallel to the x direction of the array, a ratchet effect is observed for an ac long the x direction leading to vortex motion along the y direction, along which the potential is asymmetric.…”

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confidence: 99%

Rocking ratchet induced by pure magnetic potentials with broken reflection symmetry

Lara

Castaño

et al. 2009

Phys. Rev. B

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A ratchet effect ͑the rectification of an ac injected current͒ which is purely magnetic in origin has been observed in a superconducting-magnetic nanostructure hybrid. The hybrid consists of a superconducting Nb film in contact with an array of nanoscale magnetic triangles, circular rings, or elliptical rings. The arrays were placed into well-defined remanent magnetic states by application of different magnetic field cycles. The stray fields from these remanent states provide a magnetic landscape which influences the motion of superconducting vortices. We examined both randomly varying landscapes from demagnetized samples and ordered landscapes from samples at remanence after saturation in which the magnetic rings form parallel onion states containing two domain walls. The ratchet effect is absent if the rings are in the demagnetized state or if the vortices propagate parallel to the magnetic reflection symmetry axis ͑perpendicular to the magnetic domain walls͒ in the ordered onion state. On the other hand, when the vortices move perpendicular to the magnetic reflection symmetry axis in the ordered onion state ͑parallel to the domain walls͒ a clear ratchet effect is observed. This behavior differs qualitatively from that observed in samples containing arrays of triangular Ni nanostructures, which show a ratchet of structural origin.

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“…These results represent a clear and unambiguous evidence that the observed ratchet is genuinely magnetic in origin. The demonstration of vortex ratchets induced by triangular rings is particularly interesting because, whereas the bars cannot be demagnetized in a straightforward way, the triangles could be easily induced into a magnetic vortex state [13] which erases the total magnetic moment in every element, thus providing a reliable way to switch off the ratchet effect. On the other hand, microbar arrays present a simpler magnetic texture, suitable for understanding the magnetic-dipole ratchet mechanism.…”

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Dipole-Induced Vortex Ratchets in Superconducting Films with Arrays of Micromagnets

et al. 2007

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We investigate the transport properties of superconducting films with periodic arrays of in-plane magnetized micromagnets. Two different magnetic textures are studied: a square array of magnetic bars and a close-packed array of triangular microrings. As confirmed by magnetic force microscopy imaging, the magnetic state of both systems can be adjusted to produce arrays of almost pointlike magnetic dipoles. By carrying out transport measurements with ac drive, we observed experimentally a recently predicted ratchet effect induced by the interaction between superconducting vortices and the magnetic dipoles. Moreover, we find that these magnetic textures produce vortex-antivortex patterns, which have a crucial role in the transport properties of this hybrid system. DOI: 10.1103/PhysRevLett.98.117005 PACS numbers: 74.78.Na, 05.40.ÿa, 74.25.Fy, 85.25.ÿj Nanoengineered arrays of vortex pinning sites have recently spawned numerous novel phenomena and potential applications based on vortex manipulation in superconductors. These structures are very suitable for tailoring the critical current and equilibrium properties [1-3] as well as for manipulating the distribution and direction of motion of flux quanta in superconducting devices [4 -7]. Such a control of vortex motion can be achieved when the periodic pinning potential lacks the inversion symmetry in a given direction, in which case any correlated fluctuating force induces a net vortex motion based on the phenomenon known as ratchet effect [8].As recently proposed by Carneiro [9], a different way to create vortex ratchets can be realized by using in-plane magnetized dots. Here the spatial inversion symmetry is broken not by the shape of the pinning sites but rather by the vortex-magnetic-dipole interaction. This dipoleinduced ratchet motion depends on the orientation and strength of the local magnetic moments thus allowing one to control the direction of the vortex drift. It is particularly this flexibility to manipulate the vortex motion which makes this kind of pinning potentials attractive for practical applications, although still a clear experimental corroboration is pending. In the present work, we demonstrate in a series of transport experiments that in-plane magnetized dipoles can indeed rectify vortex motion. Moreover, the rectified voltage induced by the ratchet motion depends strongly on temperature and field intensity and is nonzero even at zero field. Our analysis suggests that this behavior results from the interaction between the external field-induced vortices and vortex-antivortex pairs generated by magnetic dipoles.Our measurements were performed on two samples with different magnetic templates: (i) a 50 nm thick Al film with an on-top square array (period a p 3 m) of Si=Co=Au bars (with thicknesses 5 nm=47 nm=5 nm and lateral dimensions 2:6 0:5 m 2 ), labeled Bar-Al, and (ii) a Ge=Pb=Ge trilayer (20 nm=25 nm=5 nm thick) evaporated on top of a close-packed square array of equilateral triangular Co rings (250 nm wide, 23 nm thick, with lateral siz...

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Tunable pinning in superconducting films with magnetic microloops

Cited by 29 publications

References 15 publications

Switchable magnetic dipole induced guided vortex motion

Switchable magnetic dipole induced guided vortex motion

Rocking ratchet induced by pure magnetic potentials with broken reflection symmetry

Dipole-Induced Vortex Ratchets in Superconducting Films with Arrays of Micromagnets

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